


Initiation

by Korazan



Category: Katekyou Hitman Reborn!
Genre: Don’t copy to another site, M/M, Mates, Mpreg
Language: English
Status: Completed
Published: 2019-07-05
Updated: 2019-07-05
Packaged: 2020-06-09 17:22:45
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,715
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19480546
Author URL: https://archiveofourown.org/users/Korazan/pseuds/Korazan
Summary: [ONE-SHOT] Tsuna was supposed to return soon. He was strong, no problem taking care of his target. But he took months to finally come back… And he wasn't alone. [R27]





	Initiation

**Author's Note:**

> It's been a while, isn't it! Hello everyone! :D I'm not dead, but I've found a job and it of course gets hard to find time to write in peace :/
> 
> I'll use this chance to give some news:
> 
> -Family's new chap is coming along, sorry for making you wait but I don't want to rush things and then the chap turns out badly :/
> 
> -New stories are almost complete!
> 
> -If you want to follow my progress real time then join me on discord, we could chat or exchange fanfictions to read :) You can find the link on my profile page, I'll add more just in case one doesn't work, just take off the underscores or PM me :)
> 
> Now, on to this story, the usual warnings, if you want, read them, else, skip them and enjoy the surprises :D I don't remember how this idea came to be. I was surfing through my notes, found it and my Muse decided she wanted it to be written. So, here it is, just like with The Mission :)
> 
> WARNINGS:
> 
> \- shounen-ai, mpreg, rated M to be safe
> 
> \- merfolk!characters, not everyone
> 
> \- Mates' mechanics (no A/B/O)
> 
> \- Really simple and short, one-shot
> 
> \- R27, one-sided all27
> 
> \- Iemitsu's adorable idiocy
> 
> \- Nana's not so oblivious or weak
> 
> Words: 3698.
> 
> Enjoy!

"He's taking too loooooong..!"

"Dear, it took you more than a year to return."

"Buuuut..!"

Nana fondly shook her head at him, all the while petting Natsu. "But?"

"It's already been ten months three days six hours and…. 34 minutes!" Iemitsu pouted like a child denied his candies and threw his hands in the air. "It shouldn't take this long! Sure, his target's dangerous and all, but my _adorable_ Tuna-fishie is strong!"

Nana hummed with a smile. "Of course he is, but maybe something went wrong, we don't know." She tried to reason.

"And I can't go to check on him…"

"Rules don't allow that."

Iemitsu returned to his moans about missing his son and she sighed. This had started one month after Tsuna's departure, it was becoming really annoying despite how much she loved her mate. Even Natsu showed signs of irritation, and he had patience that rivalled Tsuna's, as in the one of a saint.

Dear son of her… She hoped he was fine. His Initiation had turned out to be quite the hassle. She remembered her own and had to wipe a smirk off her face. Her appearance sure comes in handy when hunting down humans.

"Honey, you're scaring the guards."

Nana yelped. "O-oh… sorry, I was reminiscing."

"No worries… MY TUNA-FISHIE! WHERE ARE YOU?!"

She sighed, hoping that Tsuna was indeed about to come back. As per rules, contacts during the Initiation were forbidden. The first hunt was to be carried alone, without aid and independently. Iemitsu's target had been a kung-fu master. Quite a difficult task, if considering the distance from their home. Her target, instead, had been a womanizer… so easy to kill, really.

"Dear, he can't come back before killing his prey. Just have faith in him, the human is strong."

Iemitsu sniffed, tightly hugging a miniature doll of Tsuna to his chest. He was so adorable like that. "B-but… What if…"

"What if… what? Tsuna is strong, he can kill him with no problem."

"Then why is he taking so loooong…..?"

Nana shrugged. "Maybe he's sneaky, hard to catch. Or maybe he's far from the sea, you should know how that complicates things."

"I have a bad feeling…"

She narrowed her eyes. "Bad-bad or bad-good?" He looked away. "Iemitsu." He flinched, throwing her the puppy eyes. "No way it works now. Answer the question." Tsuna was _her son_. She should know if things were bad-bad.

"… bad-good…" She sighed in relief.

"You gave me a fright there, dear." Nana patted Natsu and he moved from her lap, laying on the ground. "Come here." She widened her arms and Iemitsu approached her with a pout, crossing his arms on her lap.

Nana started cradling her fingers through his hair, earning appreciating sounds. "I want my son back…"

"Me, too. We just need to wait. Your Intuition would warn you if something bad-bad was about to happen, so just have faith in him." She smiled, plucking an old scale from her pale yellow tail and offering it to her mate.

The same thing she'd done the first time they had met. She remembered as if the day before, rushing to her duties as one of the cooks in the palace and clumsily crashing into the crown Prince. And then, they had locked eyes. Sparks had travelled through their limbs. They were mates. They could feel it in their stomachs, in their hearts, in their linking minds. They were mates and nothing would ever divide them.

Nothing ever tried.

Meeting one's mate was a difficult thing to achieve. They could be part of the merfolk, of the human race, of the animals, they could be already dead or not born yet. She hoped, one day, her Tsu-kun would find something so beautiful as sharing a moment with his mate. A beautiful lady, maybe? Or a lady-killer, she was fine with either.

She looked at her mate's dark blue tail, curled around him on the clear grey ground. "Who knows, maybe he is already on his way ba–"

Her comforting words died when a guard knocked on the doors and entered to deliver a message: "The Crown Prince has returned, he's heading this way."

Ieamitsu literally jumped with the widest smile she'd ever seen since giving birth and shouted his happiness. She shook her head, one hand on her cheek. But, if Tsu-kun was back, what was the bad-good thing about? It meant that something would go bad, but end up good. Uhm…

Her mate regained his control and went to sit at her side on the throne, taking her hand in his, beaming like a child with his favourite toy. Natsu turned to the door and waited, but his mood had visibly improved, too. It was sad to leave back a spirit animal, but it had to be done, poor thing.

With trepidation, Iemitsu started tapping the free fingers on the throne but didn't lose his brightness. The doors opened again after a while and her Tsu-kun came in. The first thing Nana registered were the human legs. Although she didn't mind them and they were undoubtedly useful, it was strange for her son to keep them instead of his strikingly beautiful tail, with scales the shades of gold and sunset-orange. Next, she noticed a small bundle in his arms, cradled protectively against his bare chest as he was wearing just a pair of skinny pants. Tsuna's always been one for tight clothes and everyone on the ocean floor never ceased to appreciate that. She admitted his son could be sexy if he wanted to be.

But her eyes stopped suddenly at the addition following his son like a looming shadow. A young human, dark hair and darker eyes, hidden behind a fedora, black like the suit he was wearing. How was he… breathing?

If she had just tensed in suspicion, her mate had become like stone.

Tsuna walked up to them and bowed curtly. "I'm back, dad, mom." He lifted a hand to the stranger. "Meet Reborn, my target."

….

_What._

Iemitsu turned back into flesh in a heartbeat, as if aunt Medusa had just flipped a switch, and stuttered something. Nana swallowed and decided to help.

"What does this mean, Tsu-kun?"

"I can't kill him."

The mermaid felt like falling into the dark depths of the ocean without her tail. "B-but, you have to… I mean, why is he… here?" Something… Something didn't feel right. Especially the smug smirk on the man's face.

"Because I wanted you to meet him. I thought it right."

No. There was something that Nana couldn't see. That she was failing to notice. She cleared her throat seeing as her mate had once again turned into a gaping coral.

"Tsu-kun, why?"

Her son looked down. The man, Reborn, came to his side and slid an arm on his shoulder, as if _protecting_ him. Tsuna moved his eyes on the other's face and nodded. He left the embrace and walked up the stairs to the throne. Nana swallowed again, feeling like this was a turning point in her son's life.

And how right she was.

Tsuna just stopped in front of her and offered the small white bundle. Unsurely, she took it with instinctive care. What she saw made her heart squeeze and her mind shut down. There, in her arms, sleeping soundly and peacefully, was a baby, female, with a short and soft blonde hair and chubby small hands softly fisted on her clothed chest. She was… she was beautiful. She felt a finger on her cheek before understanding she'd just shed a tear.

Connecting the dots, then, was child's play. Of course he could breathe.

Nana cradled her granddaughter and checked his son's mate like a hawk studying her prey. Lady-killer, alright, but he didn't waver under her gaze, so it was a good beginning. She looked at Tsuna and smiled.

"Congratulations, Tsu-kun. I guess you could have not travelled in your condition, huh?"

His son relaxed his tense shoulders and smiled back. "No. And I needed to… settle things first." He threw a thump at his mate. "He was hard to deal with."

"Tsuna…"

Iemitsu startled at the new, deep voice, blinking away his daze and refocusing at the matter at hand. His mate had just cried – a single tear, of joy, but useless details –, his son had returned from his journey, a _human_ was in his palace with crossed arms and he couldn't understand how these things were linked.

"It's true. You literally fled the first time."

"Because you tried to kill me."

"Yeah, but then…" Tsuna waggled his eyebrows and Iemitsu kind of lost it again when the stranger smirked. "You had every reason to stay."

He watched the careless shrug, noticing the hands in the pants' pocket only then. "I challenged you to find me. I'm glad you did." He tilted his head to Nana, where Iemitsu saw a ball of clothes.

Arching a brow, Intuition naturally born in the royal family blaring flashing lights in his mind, the King leaned over to understand what his mate was gently rocking in her arms. Nana noticed and stood from her chair to swim nearer. Iemitsu gulped as she bended and let him see.

Instead of stone, he turned into mushy seaweed at the super-cute child in her arms. It was like seeing Tsuna as a newly born ray of sunshine through the sea's mantle all over again. He lifted one hand and let a finger trace her soft cheek with utmost care. She was so beautiful and precious and bright and delicate and…

"Dear…" He looked up at Nana with tears in his eyes. "I think we've just become grandparents."

Everything shattered.

Well… Kind of.

 _Who_ had had the _guts_ to touch his _untouchable_ son.

His eyes looked at the human and narrowed dangerously.

Nana wisely cradled the baby back in her arms and smiled sweetly at her, uncaring what unfolded to the one that had, effectively, got her son pregnant without even the proper courtship. Not that she could talk, clear, but he understood her mate's desire to strangle the smug man now looking down at him even if he was _lower_ than them

"You."

Tsuna intercepted everything.

"Dad."

Iemitsu knew that tone. It was remarkably similar, if not the _same_ , of his mate's one when she got so mad she couldn't even try to keep her killing intent down. Tsuna did a better job at hiding it, but not the tone. No, the tone could have made his brother Xanxus cower in fear.

"This man is Reborn…" So much like his mother. "… he is my mate…" …. Wha– "… and the father of my daughter." Tsuna pointed at Nana. " _Your_ granddaughter, dad."

Yeah, he had… understood… that point? What…?

Iemitsu had to turn again to his mate, eyes falling to the bundle in her arms. The baby was moving a bit, maybe stirring from her sleep. Tsuna stepped up with a bottle of milk he had produced from who knew where and gave it to the human. His son took the baby and held her to his chest, rocking her softly and humming a low tune.

The King slumped on his throne, watching Tsuna give his child to the human… to his _mate_. Damn. His son had found his mate… A human… The target…

"… How did this happen?" He finally managed to ask, watching as the human took the baby and started feeding her with _care_.

Tsuna turned to him, then looked down with a sigh. "It went well in the beginning." He started, scratching his nape. "I morphed into a human and started searching for him…" He waved a hand to his mate. "For the World's Greatest Hitman. Apparently, when you are that strong, you become less careful because you can basically kill anyone that attempts at your life." Reborn sent him a blank stare. "Don't look at me like that, you were completely open." He crossed his arms in defiance. His mate rolled his eyes. "Anyway… My plan was to kill him in his sleep… I managed to surprise him… Then he surprised me." Iemitsu religiously ignored the smirk on the black-haired man's lips. "I couldn't kill him and we…" Tsuna blushed. "Well, we are mates, so I don't _want_ to kill him." He stated.

There was a small threat in that sentence. The two guards standing at the door tensed.

"And I came only to let you know. I'm moving to the surface for the time being." Tsuna checked on his daughter and then regarded his parents. "I'll visit in some months, but Mikasa needs to grow up before we can move somewhere near the Ocean. Afterwards, we'll visit regularly, ok?"

Iemitsu gaped like a fish.

"Oh, Natsu can come, we have a fish tank big enough for a white shark in our mansion."

Nana smiled at him, recognizing the happiness she'd experienced when she'd first met her mate. She nodded in understanding and gave her son her blessings.

"Just be sure to visit, ok? We want to see her… Mikasa grow up, too, uhm?"

Tsuna hugged her and then took his baby from Reborn's arms, she'd just finished her milk. "We will. See you soon, mom, dad." He kissed Nana on the cheek and made Mikasa delicately wave her small hand.

Reborn eyed the big shark that started following them from a careful distance. Then sighed while shaking his head and sneaked an arm around Tsuna's waist.

"Spirit animal, huh…" He regarded his parents and took off his hat with a respectful nod. "Meeting you was a pleasure, Nana, Iemitsu." The King openly scowled at the lack of honorifics. "My name is Reborn and I am your son's fiancé, you're invited to our wedding taking place a year from now." Iemitsu started resembling a ticking bomb, Nana was ecstatic and was already congratulating her son and _planning_. "Oh, and I love him and our daughter, so no use worrying about that. See you."

That said, Tsuna was a blushing mess from which Reborn stole a chaste kiss. Nana squealed, the guards wanted to cry out their Crown Prince deserved better – them, for example –, Iemitsu literally cried out how his son had lost his pureness and was now prisoner of an unhealthy love with some Mafia hitman, the entire kingdom came to know about their beloved Prince's new situation and, of course, the news travelled fast to the nearby palaces. Several Kings that had _intentions_ raged over the news, some cried, some promised to take their revenge.

As a matter of fact, Nana just chuckled darkly in a corner whenever someone came to them asking to have a chance to "free the Prince from the beast keeping him imprisoned". Federico, one of her mate's brother, objected that Tsuna was supposed to kill and eat the human and become the strongest among them.

The young mermaid couldn't help but notice that her dear son had effectively eaten up his prey. Just, not in the conventional way. And he had surely become stronger.

**I wonder if you want a bonus... Uhm.. Consider this: I didn't sleep last night (damn insomnia) and these two bonus parts came along. Hope you like them :)**

**BONUS - 01**

Tsuna was speechless.

He was literally one step from getting his meal. _Literally_. He just needed to push, to sink the knife in that tense, broad neck, and it would be done. He could return home.

But this _human_ had to open his obsidian eyes, had to look at him, had to ignite a flame Tsuna didn't know he had in the pit of his stomach, in the depth of his heart. His breath stuck in his throat. The man couldn't move from his position because the brunet was effectively blocking his arms and legs with inhuman strength, so he had settled to just observe him with orbs that mesmerized the poor merman. It was… _intoxicating_.

"Just do it."

The voice sent shivers down his spine. Tsuna had to repress them and he wanted to _just do it_ , but his arms wouldn't move, they seemed made of marble, skin glistening like the seabed in the morning sun that peaked through the window. He swallowed and tried again, still nothing.

The hitman arched a brow, unamused. "So?"

Tsuna wavered. He needed to kill him, to eat him, he _wanted_ to end his life… No, he didn't _want_ to.

"I can't."

With sudden, _right_ determination, he eyed the knife, the hilt decorated with blue and violet shells, and then threw it against the wall, embedding it deeply with practiced ease. The man under him blinked a few times, surprised and unbelieving.

"Why?" He asked after a while, unmoving.

Tsuna sighed, covering his face with one arm and letting go of the other's limbs. "Because I can't kill my mate."

He felt movement under his legs, remembering the position he was in. He'd attacked the human during his sleep, after all, so he was basically straddling a man, his _mate_. He blushed furiously and something stirred down below.

"Mate? What do you mean?"

The brunet lifted one hand and showed the particular shade of orange his skin took when basked in the sunlight. "I'm a merman, here for my first hunt on the surface. Sometimes, we meet our mates, and you are mine." He explained.

But then, he didn't know why he was explaining it at all. With a sudden urge to run away, Tsuna made to leave and cool off somewhere. He didn't expect to be pulled and feel his back collide with a soft bed. Their position had just been reversed and it did nothing useful to his awakening arousal. His blush worsened.

"Let's enjoy it, then."

Tsuna's eyes widened. "What…?"

The raven licked his lips and he couldn't control his reactions anymore. Damn if that wasn't arousing. It made Tsuna feel like a jellyfish. Those muscles, that skin, those eyes, what a sexy devil…

"We're mates, let's mate."

And it was quite easy for the man to quickly _mate_ , given their position and their lack of proper clothes. Tsuna lost it.

Waking up in the bed alone made the brunet merman annoyed. The hitman, Reborn, had _mated_ with him more than once the night before, so Tsuna was ready to track him down and tie him up and _use_ him to get a small revenge.

He did just that, though Reborn didn't complain _at all_.

The raven showed a face when Tsuna discovered he was pregnant. With how many times they had _mated_ , it was not so surprising. Turned out his mate didn't know mermen could bear children.

Well, surprise surprise.

For a moment, the brunet actually thought Reborn would have ran away again. He was wrong. Not only did his mate take this seriously, he even started to enjoy it and they got along even too well. So well that he once said: "The more, the merrier." And Tsuna _knew_ it was referred to having a lot of children.

He agreed.

**BONUS - 02**

To say that the whole Kingdom – and the nearby ones – was grieving would be a grave understatement.

Everyone, male and female, was just _thorn inside_ by knowing their dear, beloved, sexy, beautiful Prince had found his mate. Some understood its meaning and were happy, though also sad, for him. Some wanted justice, because his mate was a _human_.

Mostly, the other Princes were completely unable to acknowledge the news.

A certain Dino, from the Seahorses Kingdom, would be seen crying on a grave with the cravings: "Here lies my love for Tsunayoshi, a pearl stolen from the sea by a Barbarian." Not his guards, not even his most trusted Romario, could get him to move from there for an entire week.

A bit farther to the North, Enma of the Turtles knelt on the seabed for hours, listening to his friend Adhelheid going on and on about growing a backbone and how to ask someone out. As if he wasn't already dying inside.

To its right, in the Hammerheads' clan turf, Kyouya beat up to a pulp countless sea monsters to blow off some steam, but deep inside he was planning a full-out attack against foolish human herbivores with an army.

The nearby Albino Tribe found their stacks of marshmallows gone as their Leader drowned in his sorrow and decided to die through sugar intake.

Princesses Haru and Kyoko organized nights and nights to comfort each other with cakes, hugging each a Tsuna-sized pillow with his face printed on it.

An old retired man chuckled at the mess his youngest son was causing in one of the training rooms. Xanxus was too proud to admit out loud how much he cared for his nephew, but it was crystal clear like the water of the lake where he'd met his late mate. Oh, how Timoteo missed her. But, back to the matter at hand, Xanxus was about to destroy the sixth room that week and he needed to be stopped.

"Son."

Fury was directed at him with gaze alone. Well, his fault, he knew Xanxus didn't like to be called that, but Timoteo found it too amusing. And a good, sneaky exercise to improve his patience.

He smiled kindly at him. "Instead of depriving us of another valuable room, why don't you redirect you rage towards the right target?"

Xanxus arched an eyebrow at him. He was silent for a long time, losing his offensive stance as the scared guards scrambled off to save their scales. Amusing. His youngest was probably the scariest and the strongest, though Iemitsu could become deadly and unpredictable when angered or when his family was threatened.

"I can't kill the brat's mate."

Timoteo blinked owlishly at his son's uncharacteristic low voice. "You can't…?"

Xanxus relaxed his fisted hands and looked away. "Cut the crap. You know I cant. I don't want to–… And they're mates, it should mean…" His face showed ire again and he punched the reinforced wall. "Fuck! I can't! End of it! Let me be!"

With sudden understanding of what was going on in his youngest's mind, the man decided to heed to his request. Xanxus didn't want to kill Tsunayoshi's mate because he didn't want to be hated.

Who knew he could be this cute.

**Author's Note:**

> Hope you liked it :D And be sure to join me on discord for news! :D See ya next time!


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